1. Field of the Invention
This invention relates to a color information detecting device for detecting, for example, color temperature information.
2. Description of the Prior Art
Conventional image sensing devices such as video cameras, etc., control white light balance by having the gains of amplifiers disposed within different color or chroma signal channels preset to bring chroma signal components into a ratio of 1:1. This is accomplished either by attaching a white cap to the lens of the camera or by directing the lens of the camera toward a white object. These white balance control methods, however, degrade the operability of the camera to a great degree.
To solve this problem, proposals have been made to use a color temperature detector arranged to constantly detect the color temperature of an object to be photographed. The gain of each color or chroma signal channel is adjusted as necessary on the basis of the output of this color temperature detector. The color temperature detector uses, for example, an R sensor for detecting the red (R) component of light coming from an object and a B sensor for detecting the blue (B) component of the light. The color temperature detector obtains color temperature information from the ratio of the outputs of the two sensors. The operation of the color temperature detector is based on the premise that the ratio of the R and B signals thus obtained corresponds to the color temperature as a single-valued function. However, in this conventional color temperature detector, the R and B sensors must be arranged to receive the light from the same light source in the same manner. This requirement has necessitated overlapping the two sensors in a multi-layer form. More specifically, for example, an n-type silicon layer, a p-type silicon layer, and an n-type silicon layer, are dispersed on a semiconductor substrate. Electric charges corresponding to light incident on the junctions between them are read out. Red and blue components are primarily detected in the junction near the surface while the red component is detected in the junction farther away from the surface of the substrate. This arrangement is based on the premise that light of a short wave length does not reach the deep part of a semiconductor substrate. In accordance with this arrangement, however, the spectral characteristics for the color detectable by the two sensors are not constant. Accordingly, errors result.
Conceivably such errors may be avoided, and the spectral characteristics be made constant and reliable, by forming the light receiving faces of the R and B sensors into shapes such as shown in FIG. 1 of the accompanying drawings. In FIG. 1, the R sensor has a light receiving face R20, and the B sensor a light receiving face B20. The two light receiving faces are arranged independently of each other on the same plane. The centers R-C and B-C of the sensitive portion of these light receiving faces are completely separated from each other.
With the sensors arranged in this manner, when a part of the camera casing 9 blocks or eclipses light from the light source, as shown in FIG. 2, the ratio of the outputs of these sensors is erroneous and hinders accurate color temperature measurement. This problem is most acute when the boundary line Y between the light receiving faces R20 and B20, an edge of the camera casing and the light source, which are shown in FIG. 2, happen to be in alignment.